diff options
Diffstat (limited to 'doc/src/sgml/rules.sgml')
| -rw-r--r-- | doc/src/sgml/rules.sgml | 40 |
1 files changed, 21 insertions, 19 deletions
diff --git a/doc/src/sgml/rules.sgml b/doc/src/sgml/rules.sgml index d229b94d396..784c16e76ea 100644 --- a/doc/src/sgml/rules.sgml +++ b/doc/src/sgml/rules.sgml @@ -797,9 +797,9 @@ SELECT t1.a, t2.b, t1.ctid FROM t1, t2 WHERE t1.a = t2.a; <para> What happens if a view is named as the target relation for an - <command>INSERT</command>, <command>UPDATE</command>, or - <command>DELETE</command>? Doing the substitutions - described above would give a query tree in which the result + <command>INSERT</command>, <command>UPDATE</command>, + <command>DELETE</command>, or <command>MERGE</command>? Doing the + substitutions described above would give a query tree in which the result relation points at a subquery range-table entry, which will not work. There are several ways in which <productname>PostgreSQL</productname> can support the appearance of updating a view, however. @@ -813,11 +813,12 @@ SELECT t1.a, t2.b, t1.ctid FROM t1, t2 WHERE t1.a = t2.a; If the subquery selects from a single base relation and is simple enough, the rewriter can automatically replace the subquery with the underlying base relation so that the <command>INSERT</command>, - <command>UPDATE</command>, or <command>DELETE</command> is applied to - the base relation in the appropriate way. Views that are - <quote>simple enough</quote> for this are called <firstterm>automatically - updatable</firstterm>. For detailed information on the kinds of view that can - be automatically updated, see <xref linkend="sql-createview"/>. + <command>UPDATE</command>, <command>DELETE</command>, or + <command>MERGE</command> is applied to the base relation in the + appropriate way. Views that are <quote>simple enough</quote> for this + are called <firstterm>automatically updatable</firstterm>. For detailed + information on the kinds of view that can be automatically updated, see + <xref linkend="sql-createview"/>. </para> <para> @@ -827,10 +828,10 @@ SELECT t1.a, t2.b, t1.ctid FROM t1, t2 WHERE t1.a = t2.a; Rewriting works slightly differently in this case. For <command>INSERT</command>, the rewriter does nothing at all with the view, leaving it as the result relation - for the query. For <command>UPDATE</command> and - <command>DELETE</command>, it's still necessary to expand the + for the query. For <command>UPDATE</command>, <command>DELETE</command>, + and <command>MERGE</command>, it's still necessary to expand the view query to produce the <quote>old</quote> rows that the command will - attempt to update or delete. So the view is expanded as normal, + attempt to update, delete, or merge. So the view is expanded as normal, but another unexpanded range-table entry is added to the query to represent the view in its capacity as the result relation. </para> @@ -842,13 +843,13 @@ SELECT t1.a, t2.b, t1.ctid FROM t1, t2 WHERE t1.a = t2.a; list to identify the physical locations of the rows to be updated. This does not work if the result relation is a view, because a view does not have any <acronym>CTID</acronym>, since its rows do not have - actual physical locations. Instead, for an <command>UPDATE</command> - or <command>DELETE</command> operation, a special <literal>wholerow</literal> - entry is added to the target list, which expands to include all - columns from the view. The executor uses this value to supply the - <quote>old</quote> row to the <literal>INSTEAD OF</literal> trigger. It is - up to the trigger to work out what to update based on the old and - new row values. + actual physical locations. Instead, for an <command>UPDATE</command>, + <command>DELETE</command>, or <command>MERGE</command> operation, a + special <literal>wholerow</literal> entry is added to the target list, + which expands to include all columns from the view. The executor uses this + value to supply the <quote>old</quote> row to the + <literal>INSTEAD OF</literal> trigger. It is up to the trigger to work + out what to update based on the old and new row values. </para> <para> @@ -857,7 +858,8 @@ SELECT t1.a, t2.b, t1.ctid FROM t1, t2 WHERE t1.a = t2.a; <command>UPDATE</command>, and <command>DELETE</command> commands on a view. These rules will rewrite the command, typically into a command that updates one or more tables, rather than views. That is the topic - of <xref linkend="rules-update"/>. + of <xref linkend="rules-update"/>. Note that this will not work with + <command>MERGE</command>, which currently does not support rules. </para> <para> |